libstdc++: Fix noexcept-specifier for ranges::empty

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
libstdc++-v3/ChangeLog:

	* include/bits/range_access.h (ranges::empty): Check whether
	conversion to bool can throw.
	* testsuite/std/ranges/access/empty.cc: Check for correct
	noexcept-specifier.

(cherry picked from commit f9598d89a9f5a327ecdfa6f6978a0cfbe4447111)

diff --git a/libstdc++-v3/include/bits/range_access.h b/libstdc++-v3/include/bits/range_access.h
index 36bc55e6559af34ab52543beb42f8047a294dd6e..aee72c3fae40bcba5ea8bf12b34339ea94f61394 100644 (file)
--- a/libstdc++-v3/include/bits/range_access.h
+++ b/libstdc++-v3/include/bits/range_access.h
@@ -773,7 +773,7 @@ namespace ranges
        _S_noexcept()
        {
          if constexpr (__member_empty<_Tp>)
-           return noexcept(std::declval<_Tp>().empty());
+           return noexcept(bool(std::declval<_Tp>().empty()));
          else if constexpr (__size0_empty<_Tp>)
            return noexcept(_Size{}(std::declval<_Tp>()) == 0);
          else

diff --git a/libstdc++-v3/testsuite/std/ranges/access/empty.cc b/libstdc++-v3/testsuite/std/ranges/access/empty.cc
index 4b54ed7b36780009453c2fe837454fc408f8dbc0..47dfca6513f9ef93338588b13a119d1cfdd3827f 100644 (file)
--- a/libstdc++-v3/testsuite/std/ranges/access/empty.cc
+++ b/libstdc++-v3/testsuite/std/ranges/access/empty.cc
@@ -68,9 +68,40 @@ test02()
   VERIFY( !std::ranges::empty(so) );
 }
 
+void
+test04()
+{
+  struct E1
+  {
+    bool empty() const noexcept { return {}; }
+  };
+
+  static_assert( noexcept(std::ranges::empty(E1{})) );
+
+  struct E2
+  {
+    bool empty() const noexcept(false) { return {}; }
+  };
+
+  static_assert( ! noexcept(std::ranges::empty(E2{})) );
+
+  struct E3
+  {
+    struct B
+    {
+      explicit operator bool() const noexcept(false) { return true; }
+    };
+
+    B empty() const noexcept { return {}; }
+  };
+
+  static_assert( ! noexcept(std::ranges::empty(E3{})) );
+}
+
 int
 main()
 {
   test01();
   test02();
+  test04();
 }